Error diagnoses for managing complex mechatronic systems require model-based diagnostic procedures. Depending on whether a model-based diagnostic function or a model-based diagnostic algorithm is calculated on-board (on-line), i.e., within the system, or off-board (off-line), i.e., outside of the system, a differentiation is made between two basic diagnostic concepts, namely on-board error diagnosis and off-board error diagnosis.
In principle, only a traditional on-board error diagnosis is capable of ensuring an unambiguous error diagnosis based on complete informational content concerning a time behavior of a faulty system. However, this is not feasible in complex mechatronic systems due to stringent real-time requirements and the simultaneously marginally available computational power in present-day control units.
Off-board error diagnosis represents a compromise which does allow computational implementation of even complex diagnostic algorithms; however, in principle, it operates only with incomplete informational content of the time behavior of the faulty system. The achievable quality of off-board diagnosis therefore turns out to be generally lower than in the case of on-board error diagnosis. Sporadically occurring errors such as, for example, intermittent interruptions due to rain water in electrical plug contacts, freezing of movable mechanical elements, overheating due to unforeseen system load, etc., cannot be diagnosed reliably; in addition, off-board error diagnosis is unambiguous only in specific error cases.
German Patent Application No. DE 103 33 171 A1 describes a model-based diagnostic method for monitoring a subsystem of a machine. A quantitative model of the subsystem is used and an event-discrete analysis of the behavior of output signals is performed using qualitative values.